I am asking this again cuz I didnt get an answer, Character is not a valid member what should I do?

local function equipPet(player,pet)
	
	local character =  player.Character--problem is here

	if pet ~= nil and character ~= nil then
		
		if character:FindFirstChild(player.Name.."'s pet") then character[player.Name.."'s pet"]:Destroy() end
		
		if character.HumanoidRootPart:FindFirstChild("attachmentCharacter")then 
			character.HumanoidRootPart:FindFirstChild("attachmentCharacter"):Destroy() 
		end

		pet.Name = player.Name.."'s pet"		

		pet:SetPrimaryPartCFrame(character.HumanoidRootPart.CFrame)

		local modelSize = pet.PrimaryPart.CFrame
		
		local attachmentCharacter = Instance.new("Attachment")
		attachmentCharacter.Visible = false
		attachmentCharacter.Name = "attachmentCharacter"
		attachmentCharacter.Parent = character.HumanoiRootPart
		attachmentCharacter.Position = Vector3.new(1,1,0) + modelSize

		local attachmentPet = Instance.new("Attachment")
		attachmentPet.Visible = false
		attachmentPet.Parent = pet.PrimaryPart
		
		local alignPosition = Instance.new("AlignPosition")
		alignPosition.MaxForce = 25000
		alignPosition.Attachment0 = attachmentPet
		alignPosition.Attachment1 = attachmentCharacter
		alignPosition.Responsiveness = 25
		alignPosition.Parent = pet.PrimaryPart

		local alignOrientation = Instance.new("AlignOrientation")
		alignOrientation.MaxTorque = 25000
		alignOrientation.Attachment0 = attachmentPet
		alignOrientation.Attachment1 = attachmentCharacter
		alignOrientation.Responsiveness = 25
		alignOrientation.Parent = pet

		pet.Parent = character
	

	end
	


end



game.Players.PlayerAdded:Connect(function(player)
	local inventory = Instance.new("Folder")
	inventory.Name = "PetInventory"
	inventory.Parent = player

	local equippedPet = Instance.new("StringValue")
	equippedPet.Name = "EquippedPet"
	equippedPet.Parent = player	

	player.CharacterAdded:Connect(function(char)
		if game.ReplicatedStorage:WaitForChild("Pets"):FindFirstChild(equippedPet.Value)then
			equipPet(player,game.ReplicatedStorage:WaitForChild("Pets"):FindFirstChild(equippedPet.Value):Clone())
		end	
	end)

	equippedPet.Changed:Connect(function()
		if equippedPet.Value ~= nil then
			if game.ReplicatedStorage:WaitForChild("Pets"):FindFirstChild(equippedPet.Value)then
			equipPet(player,game.ReplicatedStorage:WaitForChild("Pets"):FindFirstChild(equippedPet.Value):Clone())
			end
		end
	end)
	wait(5)
	equipPet(game.ReplicatedStorage.Pets.Storm)

end)

Problem is at line 3

Try This

local function equipPet(player,pet)
    repeat wait() until game:GetService('Players'):FindFirstChild(player).Character
    local character =  game:GetService('Players'):FindFirstChild(player).Character
	
    if pet ~= nil and character ~= nil then

        if character:FindFirstChild(player.."'s pet") then character[player.."'s pet"]:Destroy() end

        if character.HumanoidRootPart:FindFirstChild("attachmentCharacter")then 
            character.HumanoidRootPart:FindFirstChild("attachmentCharacter"):Destroy() 
        end

        pet.Name = player.."'s pet"        

        pet:SetPrimaryPartCFrame(character.HumanoidRootPart.CFrame)

        local modelSize = pet.PrimaryPart.CFrame

        local attachmentCharacter = Instance.new("Attachment")
        attachmentCharacter.Visible = false
        attachmentCharacter.Name = "attachmentCharacter"
        attachmentCharacter.Parent = character:WaitForChild('HumanoiRootPart')
        attachmentCharacter.Position = Vector3.new(1,1,0) + modelSize

        local attachmentPet = Instance.new("Attachment")
        attachmentPet.Visible = false
        attachmentPet.Parent = pet.PrimaryPart

        local alignPosition = Instance.new("AlignPosition")
        alignPosition.MaxForce = 25000
        alignPosition.Attachment0 = attachmentPet
        alignPosition.Attachment1 = attachmentCharacter
        alignPosition.Responsiveness = 25
        alignPosition.Parent = pet.PrimaryPart

        local alignOrientation = Instance.new("AlignOrientation")
        alignOrientation.MaxTorque = 25000
        alignOrientation.Attachment0 = attachmentPet
        alignOrientation.Attachment1 = attachmentCharacter
        alignOrientation.Responsiveness = 25
        alignOrientation.Parent = pet

        pet.Parent = character


    end



end



game.Players.PlayerAdded:Connect(function(player)
    local inventory = Instance.new("Folder")
    inventory.Name = "PetInventory"
    inventory.Parent = player

    local equippedPet = Instance.new("StringValue")
    equippedPet.Name = "EquippedPet"
    equippedPet.Parent = player 

    player.CharacterAdded:Connect(function(char)
        if game.ReplicatedStorage:WaitForChild("Pets"):FindFirstChild(equippedPet.Value)then
            equipPet(player,game.ReplicatedStorage:WaitForChild("Pets"):FindFirstChild(equippedPet.Value):Clone())
        end 
    end)

    equippedPet.Changed:Connect(function()
        if equippedPet.Value ~= nil then
            if game.ReplicatedStorage:WaitForChild("Pets"):FindFirstChild(equippedPet.Value)then
            equipPet(player.Name,game.ReplicatedStorage:WaitForChild("Pets"):FindFirstChild(equippedPet.Value):Clone())
            end
        end
    end)
    wait(5)
    equipPet(game.ReplicatedStorage.Pets.Storm)

end)